Gas generating apparatus



R.. M. MEAD I GAS GENERATING APPARATUS Feb. 13, 1940.A

Filed March 5, 1`938 I .Al

Hagi/.Mead 74; m

Patented Feb. 13, 1940 UNiTEDs'rAri-:s PATENT OFFICE I 2.19am I css dramma mm'rus American a corporation of 0hio Application March 5, 1938. Serial No. 194,180 6 Clahns. (Cl. 621i 'me distribution of liquefied gas w misma consumers has now become an accepted practice.l

Hydrocarbon gases, such as propane and butane, may be readily liquefied and vaporlze at relatively low temperatures, providing a reliable source of fuel gas. The gas in liquefied form is usually delivered to a storage tank on the customers premises from time to time by tank cars or trucks. 'I'he storage tanks are usually buried in the ground, but may also be disposed on the surface. In either case, the liqueiled gas vaporizes and builds up a substantial pressure in the storage tank by abmrbing heat from the surrounding medium. temperature changes, the tanks are usually buried below the frost line.

The rate of vaporization of the liquened gas depends on the amount of heat labsorbed. When 'a storage tank of conventional design is substantially full of liquefied gas, the body of liquid absorbs heat from the ground through practically the entire surface area of the tank. When the liquid levellfalls due to consumption of the gas, the surface of the body of fluid exposed to heat absorption is correspondingly reduced. This decreases the rate of evaporation and lowers the pressure of the gas in the tank.

I have invented .an apparatus for maintaining liquefied gas contained in an underground storage tank, in contact with a .greater portion of the surface area of the tank than would be covered by the liquid lat its natural level determined by the volume. of liquid in the tank. Expressed in slightly different language, the invention makes it possible to cause a portion of the liquefied gas in the storage tank to be disposed in heat-exchange contact with a portion of the tank wall above the level at which thewolumeiof liquidyin the tank woulshotherwile stand. In a preferred form of the invention,`I provide a tank having a double wall extending over at least a portion of its surface providing storage and vaporizing chambers. Filling connections extend through the inner wall and a gas offtake is connected to the outer wall or to a dome communicating therewith. I also provide a connection between the space within the inner wall and, that between the inner wall and the outer wall, whereby liquefied gas may flow under the vapor pressure existing in the space within the inner wall. from said space into the space between the walls. The liquid filling the interwall space absorbs heat from an area of the surrounding'earth considerably greater than that to which liquid would be exposed if permitted In order to avoid seasonal.

u.' una, Asheville, N. c., mimmto Gas Service Company, Ilma, Ohio,

to find its natural level in the inner tank. Furthery details of the apparatus and its operation will be described herebelow with reference to the accompanying drawing, the single ligure of which is a largely ldiagrammatic view showing in section a buried tank embodying the invention and the filling and delivery connections thereto.

Referring in detail to the drawing, the illustrated embodiment of the invention comprises a tank Il, having an inner container II, denning a storage space indicated generally at I2. An outerfwall or shell I3 partly surrounds the container II and is spaced therefrom deiixiing an intermediate vaporlzing space Il. I prefer to leave aportion of the surface of the container II exposed to the surrounding medium as indicated at I5. The shell or outer wall I3 is preferably provided with a dome I6 defining a space I1 for the accumulation of gas.

Filling pipes Il extend downwardly from the surface of the ground through the outer shell Il and the wall of the innercontainer II land are provided with valves I9. A gas oiftake 20 extends upwardly from the dome IB land has a main control valvel2I connected therein.

A pipe 22 extends upwardly from substantially the bottom of the space I2 through the wall of the container Il to a point about midway of the height of the dome I6. The purpose of this connection will be explained later. A vent and overflow pipe 22 extends downwardly through the shell Il and the wall of thecontainer II from a point inthe dome I6 at or slightly below the level of the top of the pipe 22,. The pipe 23 has a seat 24 at the upper. end thereof cooperating with a valve 25. The valve is carried on .a pivoted arm 26 adapted to/be actuated by a float 214 when the liquid rises in the, dome Il to the level indicated at 28.

` In explaining the operation of the invention, it will be assumed, first, that the double wall tank is being illled for the rst time and, contains.

air only. The tank is nlled by connecting a tank truck or other portable container having a supply of liquefied gas therein to one of the pipes I S, and opening the valve I9 valve II in the other pipe I8 is opened to vent the air content' as the container II is fllled. The valve 2l should be closed while filling the container. stantially filled, both valves I9 are closed. Vaporization of the liquefied gas commences immediately since the boiling point ofthe liquefied gas usually employed is lower than the normal temperature of the earth below the frost line.

lAt 30 F., for example,` certainv liqueiled fuel When the container II has been subtherein. 'Ihe gases have a vapor pressure of four or five pounds per square inch 4above that of the atmosphere. If lthe container II is initially nlled` to a level a0 l such as that indicated at 29, the pressure in the space above the surface of the liquid will build up -as soon as valves I8 are closed, to a value suilicient to cause liquid to ilow upwardly through the pipe 22 and overflow into the space I4. It will be understood that the initial evolution of vapor in the space above the liquid in the con'- tainer II is caused by heat absorbed largely through the portion I5 oi' the container wall. In order to cause liquid to ow upwardly through the pipe 23, it is obvious that a pressure diierliquid in the space I4 thus-proceeds even, more rapidly than that'within the container II. 'I'his causes the pressure in the dome I6 to build up promptly. Fuel gas inthe form of vapor may now be'drawn from the dome I6 by opening the valve 2|. 'Ihe system should be purged of air before being connected to burners.

Assuming that before the valve 2I is opened, the temperatures and pressures in the spaces I2 and II have become equalized, now of liquid up- 'wardly through the pipe 22 willcease'. When the valve 2| is, opened, however, the resulting outy ilow of .gas-from the dome I8 causes a drop in the pressure and temperature in the space I'I, and if the amount of gas withdrawn is suilicient, the differential pressure necessary to cause resumption of the liquid flow upwardly through the pipe 22 will be established. If the gas is withdrawn from the dome I6 at a rate' such as to cause .the liquid to rise to the level 2l, the float valve 25 will be opened to connect the space above the liquid in the container I I directly to the dome, thus equalizlng the pressure throughout the system and preventing further ow of liquid upwardly through the pipe 22.

'I'he iloat valve 25 vand 'vent pipe 23 may be omitted if the rate of withdrawing gas from the K dome is so limited as to prevent the liquid level rising to the-level of the connection of the pipe 20 therewith. With the iloat valve and vent pipe, it is impossible for the liquid to rise above the level 28, regardless of the rate of withdrawal of gas.

vIt will be apparent that the apparatus shown maintains a supply of liquid in thespace I 4 at all times, thus insuring that the liquid covers a greater portion of the wall of the container than would be the case if it were allowed to seek its natural level. As already explained, when no` gas is withdrawn from the dome over aconsiderable period, the temperature and pressure conditions throughout all portions of the system become equaliited. On/withdrawal of gas, however, the cooling and reduction in-pressure within the space I 'I provides the diiferential necessary to cause liquid to ilow upwardly through the pipeV 22 until temperature and pressure conditions are again equalizedor the valve 25 is opened to eiect this result. f

Rgeillling of container I I after it has been placed in operation is accomplished by connectingfone pipe I8 to the discharge port of the tank `truck and by*connecting the other pipe 4I8 to the tank liquid in the tank truck thus flows ihto the container II under the pressure existing therein. making it unnecessary to close the Vvalve 2I or shut oil. burners connected to the system while relling the container.

It will be readily appreciated that the invention provides a source of fuel gas. the pressure `of which does not vary sowidely as it does in a system comprisingan `ordinary tank. wherein the area of the tank wall covered by the li uid for heat absorption from therearth decreas as the -level of the liquid falls as a result oi consumption of gas. The invention thus provides a more satisfactory and reliable source of fuel gas for isolated consumers than has heretofore been available.

I have illustrated and described herein only one embodiment of the invention, but it will -be understood that numerous changes in the construction and arrangement shown may be made without departingfrom the spirit of the invention or the scope of the appended claims.

I claim:

1. Gas-generating apparatus comprising a container adapted to receive liqueed gas, a shell extending about at least a portion of said container, means whereby liqueed gas may be det livered to the container, means whereby liqueed gas from said container flows into the space between the container and shell, and a'valve operable when the liquid in said space reaches a predetermined level to space.

-2. A fuel-supply system comprising a storage tank. means whereby said tank may be nlled at intervals 'with liquid combustible which vaporizes vent the container to said at atmospheric temperatures, an oiitake for vapor evolving from said liquid, a shell overlying at least a portion of said tank and a pipe extending downwardly into the t nk to a point near the bottom thereof for co ducting liquid from said tank to the `space between the tank and shell when the diierential between the vapor pressures in the tank and said space increases sumciently.

3. A fuel-supply system comprising a liquid storage and evaporating tank having an outer wallin heat-exchange vcontact with a surrounding medium, means whereby said tank may be lled at intervals with liquid combustible which vaporizes at atmospheric temperatures. an oi!- take for vapor evolving from -said liquid, and means whereby the pressure of said vapor maintains a portion of said liquid in contact with the tank wall above the level of the main body of the liquid in said tank as said level falls because ofthe removal of vapor from the tank.

4. Apparatus as dened by claim 3 character- -ized by saidtank including a shell overlying at `least a portion thereof, and means for delivering liquid from the tank to the shell, said vapor offtake communicating with said shell. g

5. Apparatus asdenedby claim 3 characterized by said tank including a shell overlying at least a portion thereof, means for conveying liquid from the tank to the shell, and a collecting dome on said shell, said vapor oiItake being connected to said dome.

6. Apparatus as defined by claim 3 characterized by said tank including a shell overlying at least a portion thereof, and said means Vincluding a connection from the tank adapted to convey liquid therefrom to the space between the tank and shell when the vapor pressure in said Vspace i decreases suillciently below truck above the level of the liquid therein. The f that in said tank. ROY M. MEAD. 

